Lubrication theory

About: Lubrication theory is a research topic. Over the lifetime, 1713 publications have been published within this topic receiving 50261 citations. The topic is also known as: Fluid bearing.

Transition of frictional states and surface roughness effects in lubricated contacts

Abstract: In order to investigate frictional performances in different lubrication regimes and effects of surface roughness, the friction on engineering surfaces with different roughness patterns and amplitudes were measured. Results show a smooth transition of lubrication states from full-film hydrodynamic lubrication to mixed and boundary lubrication. Data from the tests also suggest that the transition of friction regimes is affected by roughness amplitude. It is observed that not only the smoother surfaces give rise to the lower critical velocities of transition from full-film to mixed lubrication, but also the friction coefficients at the point of the transition are much smaller for the smoother surfaces. For the transition from mixed to boundary lubrication, however, effects of roughness amplitude are insignificant. As a result, it is concluded that under the same contact conditions, different features in roughness cause the system to transit in different routines from one lubrication regime to another. Furth...

Combined thermal and electrohydrodynamic patterning of thin liquid films

Abstract: Both electric fields and temperature gradients can destabilize the surface of a thin liquid film and lead to the self-assembly of patterns composed of pillar-like structures. Such instabilities offer a relatively simple way to tailor the surface topography of coatings, which in turn can be used to influence coating appearance, texture, and functionality. The present work explores how the simultaneous application of an electric field and temperature gradient can be used to further influence thin-liquid-film instabilities. Both perfect and leaky dielectric materials are considered, and lubrication theory is applied to develop a system of nonlinear partial differential equations for the interfacial height and charge. Linear stability analysis of the lubrication equations shows that in perfect dielectric films, thermal effects tend to dominate the process, often rendering the electric field unimportant. However, in leaky dielectric films, both the thermal and electric fields play important roles and together can produce an increase in the growth rate and a reduction in the dominant wavelength of the instability. Nonlinear simulations of the lubrication equations show that the predictions of the linear theory hold even when the interfacial perturbations are no longer small. The effects of viscoelasticity are considered within the linear theory, and it is found that the growth rate of the instability, but not the length scale, depends on the rheological parameters. The findings of this work suggest that the simultaneous use of an electric field and temperature gradient will allow thin films to be patterned at length scales not accessible when only one of these destabilizing forces is used.